The present invention relates to a semiconductor device, and more particularly, it relates to a semiconductor device including a capacitor and a method for fabricating the same.
Recently, in accordance with the increased degree of integration, the improved performance and the increased speed of semiconductor integrated circuit devices, a technique to use an MIM (metal-insulator-metal) capacitor having a capacitor dielectric film made of a high dielectric constant film in a semiconductor device such as a DRAM (dynamic random access memory) has been proposed.
In order to increase the refinement and the density of a semiconductor device, it is indispensable to reduce the area occupied by a capacitor in a chip. In order to make a memory stably operate, however, a given or larger capacitance value is necessary. Therefore, by using a high dielectric constant film of a Hf oxide (HfOx) or a Zr oxide (ZrOx) as a capacitor dielectric film, a sufficient capacitance value is to be secured while reducing the area occupied by the capacitor.
In the conventional high dielectric constant film of HfOx or ZrOx, however, a state attained immediately after deposition is a polycrystalline state because of the influence of an underlying film, and a grain boundary is present in such a high dielectric constant film. Accordingly, when the semiconductor device is activated and a voltage is applied to the capacitor, a leakage current passes through the grain boundary present in the capacitor dielectric film, so as to disadvantageously easily cause dielectric breakdown of the capacitor dielectric film.
As countermeasure, a technique to suppress the leakage current in the MIM capacitor by depositing Al oxide (AlOx) on a lower electrode and forming a high dielectric constant film (of, for example, HfOx) thereon has been proposed (see Patent Document 1 below).
A method for fabricating a conventional MIM capacitor using a multilayered film composed of an AlOx film and a HfOx film as a capacitor dielectric film will now be described.
FIGS. 7A through 7F are cross-sectional views for showing procedures in the method for fabricating a conventional MIM capacitor.
First, in the procedure shown in FIG. 7A, after depositing a first interlayer insulating film 61 on a silicon substrate 60, a first hole 62 penetrating the first interlayer insulating film 61 is formed. Then, after forming a conducting plug 63 in the first hole 62, a second interlayer insulating film 64 is deposited on the first interlayer insulating film 61 and on the conducting plug 63. Thereafter, a second hole 65 penetrating the second interlayer insulating film 64 and reaching the conducting plug 63 is formed.
Next, in the procedure shown in FIG. 7B, a lower electrode material film 66A is deposited over the bottom and the inner wall of the second hole 65 so as to also cover a portion of the second interlayer insulating film 64 disposed outside the second hole 65.
Then, in the procedure shown in FIG. 7C, a portion of the lower electrode material film 66A deposited on the portion of the second interlayer insulating film 64 disposed outside the second hole 65 is removed. Thus, a lower electrode 66 with a three-dimensional structure is formed in the second hole 65.
Next, in the procedure shown in FIG. 7D, an AlOx film 67 is deposited on the lower electrode 66 by ALD (atomic layer deposition).
FIG. 8 shows a sequence for introducing reaction gases in the deposition of the AlOx film by the ALD and deposition of a HfOx film by the ALD described below.
As shown in FIG. 8, an atmospheric gas (N2) is first introduced into a chamber, and the temperature of the silicon substrate (wafer) 60 is increased. Then, a TMA (trimethyl aluminum) gas corresponding to an Al supply source is introduced into the chamber in pulsed form, so as to allow the TMA or its active species to be chemically adsorbed onto the surfaces of the second interlayer insulating film 64 and the lower electrode 66. Next, with the TMA gas stopped, a purge gas (N2) is introduced into the chamber in pulsed form, so as to remove the TMA gas remaining in the chamber. Then, after stopping the purge gas, an ozone (O3) gas is introduced into the chamber in pulsed form. At this point, the ozone gas is thermally reacted with the TMA or the active species adsorbed to the surfaces of the second interlayer insulating film 64 and the lower electrode 66, so as to produce AlOx corresponding to one atomic layer. Thereafter, the purge gas is introduced into the chamber in pulsed form again so as to remove the ozone gas remaining in the chamber. When such a sequence for depositing AlOx corresponding to one atomic layer is repeated a plurality of times, the AlOx film 67 with a desired thickness can be formed on the second interlayer insulating film 64 and the lower electrode 66.
Next, in the procedure shown in FIG. 7E, a HfOx film 68 to be used as a capacitor dielectric film is deposited on the AlOx film 67 by the ALD.
Specifically, as shown in FIG. 8, a TEMA-Hf (tetraethylmethylamino hafnium) gas corresponding to a Hf supply source is introduced into the chamber in pulsed form, so as to allow the TEMA-Hf or its active species to be chemically adhered onto the surface of the AlOx film 67. Then, after the TEMA-Hf gas is stopped, the purge gas is introduced into the chamber in pulsed form, so as to remove the TEMA-Hf gas remaining in the chamber. Next, the purge gas is stopped, and an ozone gas is introduced into the chamber in pulsed form. At this point, the ozone gas is thermally reacted with the TEMA-Hf or the active species adhered to the surface of the AlOx film 67, so as to produce HfOx corresponding to one atomic layer. Thereafter, the purge gas is introduced into the chamber in pulsed form again, so as to remove the ozone gas remaining in the chamber. When such a sequence for depositing HfOx corresponding to one atomic layer is repeated a plurality of times, the HfOx film 68 with a desired thickness can be formed on the AlOx film 67.
Next, in the procedure shown in FIG. 7F, after depositing an upper electrode material film 69 of titanium nitride or the like on the HfOx film 68, the upper electrode material film 69 is formed into an upper electrode with a desired shape.
Through the aforementioned procedures, an MIM capacitor having a capacitor dielectric film made of a multilayered film of the AlOx film 67 and the HfOx film 68 on the silicon substrate 60 is fabricated.
Patent Document 1: Japanese Laid-Open Patent Publication No. 2002-222934